The subject matter of the present application is related to an application entitled "Printed Circuit Board Having An Injection Molded Substrate" naming Hans Schmidt as the inventor, and assigned to the same assignee as the present application, identified as U.S. Ser. No. 388,818, filed Aug. 3, 1989.
The present invention relates to a printed circuit board having an injection mold substrate whose surface interconnect pattern is comprised of trench-shaped depressions in the region of interconnected traces and by planar depressions, in the region of through connection and/or connecting racks. The recessed regions have a conductive metal coat.
As will be understood by those skilled in the art, the term interconnect pattern refers to all of the electrically conductive structures which are utilized on a PC board. The term "interconnect trace" refers to the conductive path which extends between any two connection points on the board. The term "through-connections", as used herein, refers to two types of printed circuit board structures. The first structure relates to the metalized holes which connect the conductor paths of one wiring level of the PC board to another wiring level. THe second structure referred to as a "through connection" is the metalized hole which is sued to accept a component, such as a resistor lead or an integrated circuit pin, therein. Finally, the term "connecting pad" refers to the planar areas of the circuit pattern which serve, for example, for the connection of components or connecting wires.
These terms have been defined for clarification purposes only. However, the definitions set forth are not meant to be all inclusive. Accordingly, the terms should be accorded their full scope as they would be understood by those skilled in the art.
Printed circuit boards having an injection molded substrate or a similarly formed substrate are disclosed in DE-A-27 15 875 and the corresponding CA-A-107 58 25, and in U.S. Pat. No. 4,532,152.
In order to manufacture the printed circuit boards disclosed, for example, in DE-A-27 15 875, the substrate is first developed into a form in which the interconnect traces and the through-connecting holes are contained in the shape of depressions. After mechanical and/or chemical surface treatment, the substrate is then chemically activated. Once this has occurred, the raised surfaces of the substrate are covered by a protective layer. Only depressions have to remain free during the application of this protective layer. Therefore, it is no longer necessary to have an involved photo-structuring of the resist but rather the application can be done, for example, with a doctor or by roller coating. A conductive metal coat is then applied. The metal coat is preferably done by currentless metal deposition. The metal coat leads to the formation of the entire conductor configuration in the depressions of the substrate and in the through-connection holes. Finally, a solder stop lacquer is applied on the conductor surfaces which are not invalued in any solder connections.
By structuring the substrate before the selected metallization, the corresponding resist does not need photostructuring. In contrast, the application of the solder stop lacquer, requires either a selective application onto the interconnects or a photostructuring. One of these two methods are required since the planar depressions, which surround the through-contactings as solder eyes or which serve as a connecting surfaces, must remain free.